03 Feb What Tree? Blackthorn

Blackthorn (Prunus Spinosa)

Arguably blackthorn is not a tree, but rather a shrub or hedging plant, most commonly found as a key component of agricultural field boundary hedges.  The vicious, hard, sharp thorns prevent livestock from pushing through hedges while providing excellent protection for nesting birds, preventing predators from getting to them.  Tackling blackthorn without very thick gloves is for the brave or foolhardy, as the tips of the spikes will break off into exposed skin, more often than not leading to swelling and excessive pain (for the type and size of injury).  However, blackthorn is one of the first indicators that the long winter is coming to an end, with the rose petal blossom emerging before the leaves, any time from early March.  Later in the year, those flowers will have become little dark blue/purple fruits (sloes), that when picked can be added to a mixture of gin and sugar to make sloe gin.

Appearance and Identification

As a hedging shrub species, blackthorn does not grow to any meaningful height although it can attain heights of up to 5-6m.  Its most significant growth characteristic is a suckering habit meaning that it will grow outward, rapidly taking over any available open space unless well managed . It tends to grow as a thick, impenetrable tangle of twigs and branches, making it to hard to manage except by mechanical means.

The easiest time to identify blackthorn is in early Spring as it is one of the first woody stemmed plants to flower (although another member of the family, Myrobalan plum (Prunus cerasifera) will flower several weeks earlier).  Being a member of the rose family, the flower has five petals, off white in colour and frothy in appearance.  A notable characteristic of blackthorn, and a key difference with hawthorn (the other main hedge shrub) is that the flowers appear before the leaves.  If you are looking at hedges in flower, and the flower is small, off white, with five petals and you are unsure if it is blackthorn or hawthorn, look for leaves.  If leaves are present with the flowers, you are probably looking at hawthorn.   Reproduction occurs through insects carrying pollen from flower to flower, but blackthorn is a species that contains both the male and female parts within the same flower.

The bark of blackthorn is perfectly described by the common name, with the shoots being purple-black but the older stem wood being black in colour and very hard.  Sharp side shoots emerge from the twigs to form hardened thorns that will often get dense and harder if damaged through browsing or cutting.

Propagation & Control

Blackthorn is frequently planted as part of a native mix in hedging, but tends to be used in rural settings rather than domestically.  However, the sharp thorns and dense growth habit make this an excellent choice as a security feature against both unwelcome visitors in a domestic sense, and to wildlife from a biodiversity perspective.  The protection it offers to nesting birds means this could be a suitable option for planting in discreet areas of a garden, but control of the shrub is critical to limit its spread through suckering.

Source and reference materials

Information detailed in this post has been obtained from the author’s own knowledge and photographic library where possible.  Additional sources of information and photographs include:

Johnson, O & More, D (2004) Tree Guide: The most complete field guide to the trees of Britain and Europe. Collins.

Mutch, W (1998) Tall Trees and Small Woods. Mainstream Publishing

Images:

Blackthorn Flower (Wildflowerfinder)

Blackthorn leaf (Tree Guide UK)

Fruit (Sloe berry) (Pickyourownfarms)

Blackthorn hedge (Hedgesonline)

Blackthorn spine (plantidentification)

Blackthorn hedge (Positively Grounded)